High-pressure brick containing magnesia, and process of making the same



Patented Feb. 26, 1935 HIGH-PRESSURE BRICK oon'mm'mo MAG gESIA, ANDraooEss or MAKING rim Russell P. Heuer, Bryn Mawr, Pa., assignor toGeneral Refractories Company, a corporation of Pennsylvania No Drawing.Application January 9', 1934,

Serial No. 705,971 r 19 Claims.

- continuation in part of my application Serial No.

323,890, filed December 5, 1928.

A purpose of my invention is to make an unburned magnesia ormagnesia-chrome refractory brick which is equal or, superior in density,hot and cold strength, resistance to metal and slag penetration andinfusibility to the burned magnesia brick of the prior art.

A further purpose is to produce an unburned magnesia or magnesia-chromerefractory brick which, by virtue of the combination of definiteproportions of larger and smaller graded sizes, and the presence of thebond, has a high strength while the brick is at atmospherictemperatures, and which, by virtue of the small amount of bond, isrefractory at the high temperatures of use.

A further purpose is to bond an unfired magnesia or magnesia-chromebrick of very high density and very low porosity without reducing thestrength of the brick at high temperatures or rendering the brick morefusible.

A further purpose is to use 45% to 65% (preferably 52% to 58%, or better55%) of larger magnesia and/or chrome particles between 10 and mesh perlinear inch and 55% to (preferably 48% to 42%, or better 45%) of smaller magnesia and/or chrome particles through 50 mesh'per linear inch(preferably 60 mesh per linear inch, or better 80 mesh per linear inch),with an appreciable but small amount of bond, such as an acidelectrolyte (sodium acid sulphate, sodium dichromate, etc.) in thepresence of clay, or such as sodium silicate, in magnesia ormagnesia-chrome brick, and to subject the mixture of the magnesia ormagnesia-chrome particles and the bond, to molding pressure high enoughto form the mixture into a brick (1000 pounds per square inch,preferably 5,000 pounds per square inch, or better 10,000 pounds persquare inch).

A further purpose is to employ a water soluble bond between the properlysized and combined particles of an unfired magnesia or magnesia-chromebrick.

Further purposes appear in the specification and in the claims.

My invention relates to the methods involved (Cl. 25 1ss) ing theparticles into larger and smaller sizes, with the partial or completeelimination of intermediate sizes, combining the larger and smallersizes in definite proportions by weight and desirably molding under highpressure. My Patent No. 1,851,181 indicates that the introduction ofmaterial which will cause plastic floweither in the hot or cold brick isundesirable and likely to defeat the purposes sought.

In the case of an unburned magnesia or magnesia-chrome brick, which mustdevelop considerable cold strength without firing, there is a definiteadvantage in introducing a limited quantity of bond into a mix ofproperly graded and combined sizes. If the quantity of bond is limited,it need not encourage shrinkage or plastic flow in either the hot or thecold brick.

A wholly satisfactory unburned magnesia or magnesia-chrome brick can bemade without using any bond, provided the sizes of the particles areproperly graded and combined, and suitable molding procedure is used.If, to the properly graded and combined magnesia or magnesiachrome mix,a small amount of bond-be added, a definite improvement in the unburnedbrick will be noted, particularly in its strength before being subjectedto firing temperature, its subsequent cold and hot strength, and itsresistance to spalling, with little or no change in its fusibility. Alarger quantity of bond harmfully infiuences the brick, particularly byrendering it markedly more fusible, much weaker at furnace temperature,much less resistant to spalling, to abrasion, to molten slags, to.metals and to hot products of combustion, or decidedly more subject topronounced shrinkage.

In an unburned magnesia or magnesia-chrome brick, there is then anoptimum range of bond content. Without limiting myself to any theory, Imay say that I suppose that the optimum range of bond content is due tothe fact that, as soon as the bond is present in great enough quantityto actually space one non-plastic refractory particle from another, itencourages plastic flow, rendering the brick much more fusible, lessresistant to spalling and weaker at high temperatures. Shrinkage of thebond produces abnormal shrinkage of the brick. Where the bond is presentin such small amount that it merely forms a coating or film on thenon-plastic magnesia or magnesia and chrome particles, it does notappreciably space them, does not assist plastic fiow and does not reducethe high temperature properties.

Magnesia, chrome and mixtures of magnesia and chrome give good adherenceto the law of particle grading and combining as mentioned in my PatentNo. 1,851,181. It is therefore to be expected that magnesia and-magnesia-chrome brick will be advantageously affected by particlegrading and combining. To produce magnesia and magnesia-chrome brick ofhigh density and correspondingly little void space, the intermediatesize particles should be eliminated or substantially eliminated, and thelarger and smaller particles combined in proper proportions. Chromebehaves very similarly to magnesia, and my invention contemplates theuse of mixtures of magnesia and chrome in any proportions, although thepresent application is concerned more especially with mixtures ofmagnesia and chrome consisting preponderantly of magnesia. Wheremagnesia and chrome are mixed, the particles of any given size may bemixtures of magnesia and chrome particles, or the particles of that sizemay be entirely magnesia or entirely chrome, in which case the chrome ormagnesia,'as the case may be, will comprise particles of some othersize.

In order to obtain a maximum of interfitting of the non-plasticparticles, I grade the sizes of the ground refractory for making up thebrick mix into larger, intermediate and smaller particles. As only thelarger and smaller particles are preferably used in the brick, theintermediates may be reground to make smaller particles, or the systemof grinding may be so regulated that only larger and smaller particlesare produced. Obviously, if separate sources of larger and smallerparticles are available, the particles from such separate sources may beused.

Magnesia and chrome particles used by me are non-plastic. This isveryadvantageous as plastic particles have colloidally associated waterwhich renders them unsuitable for the production of brick intended foruse without burning. The colloidally associated water is driven off indrying, and during use. An unburned brick of plastic material in afurnace structure such as a furnace lining is apt to shrink and developvoid spaces during use.

The larger particles should be capable of passing a screen of 10 meshper linear inch and of being retained upon a screen of 30 mesh perlinear inch. The larger particles should preferably be between 10 and-20mesh, per linear inch, as best results are obtained when the largerparticles are of nearly uniform graded size.

The larger particles may be between 3 and 30 mesh per linear inch, or,better, between 6 and 30 mesh per linear inch. The more uniform the sizeof the larger particles, the better.

-The smaller particles should be capable of passing through a screen of50 mesh per linear inch, and preferably will pass 60 mesh per linearinch, or better mesh per linear inch. The intermediate particles, whichare substantially eliminated, will be between 30 and 50 mesh per linearinch, or preferably between 30 and 60, 30 and 80, 20 and 60, or 20 and80 mesh per linear inch.

Between 45% and 65% (preferably 52% and 58%) of larger magnesia ormagnesia-chrome particles and between 55% and 35% (preferably 48% and42%) of smaller magnesia or magnesiachrome particles should be employedto produce a magnesia or magnesia-chrome brick of high density. Thequantity of larger and smaller particles will be roughly equal. It isbest to eliminate the intermediate particles, but, less desirably, someof them, perhaps 10% or even exceed 5% of the dry brick. Sodium silicatein small amount is a suitable bond for magnesia and magnesia-chromebrick, the amount of sodium silicate being appreciable but preferablyless than 3% (5% maximum), or better, less than 4 2%. Organic bonds suchas dextrine, gum arabic or sulphite liquor (an appreciable quantity butpreferably less than 3%, or better less than 2%, or still better lessthan 1%, with 5% as a maximum) may be employed.

Magnesia and mixtures of magnesia and I chrome may be bonded by sodiumacid sulphate (sodium bisulphate) or sodium dichromate, in the presenceof clay, as explained in my U. S. Patent No. 1,859,512, granted May 24,1932. The acid electrolyte should preferably form only 2% or less (5%maximum) of the dry brick, and the clay about 2% of the dry brick, andcertainly less than 5%.

Mixtures of magnesia and chrome containing considerable chrome may bebonded by an acid electrolyte, such as sodium acid sulphate, in thepresence of finely divided magnesia, as disclosed in my U. S. Patent No.1,845,968, granted Febru ary 16, 1932. I will preferably use about 2% orless (5% maximum) of sodium acid sulphate, with about 10% of finelydivided magnesia particles for bonding purposes. 7

I contemplate that conventional brick-making methods will be used. Ihave already explained how the magnesia or magnesia and chrome particleswill be ground, graded as to size, and the larger and smaller sizes willbe combined in the proper proportions. Prior to molding the mix will besuitably moistened and the binder introduced. Where a water solublebinder such as sodium silicate or an organic substance (dextrine, gumarabic, sulphite liquor), etc., is used, a water solution of the binderwill be employed to moisten the mix and impart to the mix 5% or less ofwater soluble binder.

If desired the water solution of the binder may first be mixed with thefine particles before the coarse particles are added.

The use of high pressure for molding the brick is desirable, as the highpressure assists in producing maximum interfitting. The molding pressureshould exceed 1000 pounds per square inch, or preferably 5000 pounds persquare inch, or still better 10,000 pounds per square inch. The highpressure produces tight interfitting of the particles which developshigh density.

After molding, the brick are dried, preferably at a temperature of to300 C. This results in driving off excess moisture, but is not in anysense a burning or firing operation. The brick are now readyfor use inunburned condition.

I am aware that it is not new to bond magnesia or magnesia-chromemixtures with sodium silicate or organic binders and to use such bondedbricks in furnace linings without previous burning. I have found thatsuch unburned brick are lacking in refractoriness or strength,resistance to slag or metal attack, have undesirably high porosity orshrink in volume in service due to poor contact and interfltting -of theconstituent particlesand the presence of excessive amounts of bondingsubstance between the particles. By selecting: the proper size particlesand densely compacting them underpressure exceeding 1000 pounds persquare inch I have been able to obtain desirable brick having thenecessary particle in- .case of porosity, void space, etc. Allpercentages are based upon the dried unflred brick which is ready foruse in a furnace lining. Thus when I refer to a certain percentage ofwater soluble bond, I do not include the water which is used as avehicle for the bond, and tomoisterrthe mix,

when the bond is added, but merely mean that, of the dried .unflredbrick, the bond comprises a certain percentage by weight. 7

terfltting without burning and with a minimum A typical analysis of asuitable magnesia or of bonding substance. Such brick can be madedead-burned magnesite is: equal to or better than conventional burnedmag- Percent nesia brick. MgO (by difference) 84.50

One example of such a brick is the following CaO 4.50. composition: YF6205 5.00 Per cent A120: r 1.50 Dead burned magnesite 76 im 4.00 Chromeor 20 Loss on ignition 0.50 Ball clay 2 I Sodium bisulphate 2 100.00

A screen test of the brick mixshows:

Y Per cent On 6 mesh per linear inch Nil Thru 6 on 10 mesh per linearinch. 15

When molded under a pressure of 10,000 pounds.

per square inch and dried'at 125 C. such brick have shown a brickspecific gravity as high as 3.0 and cold crushing strengths up to 14,000pounds per square inch. As brick having a cold crushing strength ofabout 2,000 pounds per square inch may be shipped and installedcommercially, it will be evident that the unburned magnesia andmagnesia-chrome brick of my invention are amply strong. ,The brickaccording to my invention are very dense, having a porosity of less thanAccording to my invention, I procure larger and smaller particles ofmagnesia and/or chrome, add a limited quantity of the proper binderordinarily in a solution that serves to moisten the mix, mold the brick,preferably under high pressure, and dry the molded brick. 'The brick isthen ready for use in unfired condition, and may be inserted in afurnace structure such as a furnace lining, exactly like a fired brick.

Where the brick contains both magnesia and chrome, the largernon-plastic particles may be 7 entirely magnesia and the smallernon-plastic In stating percentages of magnesia and/or chrome particles,I of course intend that these percentages shall be subject to deductionfor the percentage of bond. Thus the suggested ranges of 45% to(preferably 52% to 58%) of larger non-plastic particles and 55% to 35%(preferably 48% to 42%)' of smaller non-plastic particles are subject todeductions from the lower limit in each case for the percentage of bond.

- All percentages mentioned herein are percentages by weight unless thecontext clearly indicates that they are percentages by volume, as in theIf lower quality is permissible, the lime may be greater than 7% butshould not be within the range of calcined dolomite. Magnesites may fallas low as 60% to 65% M80 content if higher amounts of CaO and FeaO: orother basic oxides are present. The magnesites may be Pr pared for'useby dead burning in kilns at about 1500" C. or by electrical fusion. 7

Whenever I mention chrome I mean chrome ore of the type used in makingrefractory brick 'or calcined chrome ore. Sodium acid sulphate.invention may be the liquid variety, water glass,

or the solid variety. When I speak of the amount of sodium silicate usedas a bond, I refer to the quantity of anhydrous sodium silicate. If asolution of sodium silicate or a hydrated solid sodium silicate be used,an increased amount of binder will be necessary to compensate for thewater present. Various commercial silicates have different ratios ofNazO to SiOz, for example, 1:4; 1:24. Such silicates are all applicableas bonding agents.

In referring to my earlier patents, I intend to incorporate theirdisclosures herein by reference and make them a part hereof.

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the structure shown, and I, therefore, claimall web in so far as they fall within the reasonable spirit and scope ofmy invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

. 1. The method of making a refractory of high density from non-plasticmaterial preponderantly magnesia, and a. bonding substance, usingnonplastic particles of relatively larger and smaller grain sizes, whichconsists in mixing larger nonplastic particles retained on a 30 mesh perlinear inch screen with smaller non-plastic particles and a bondingsubstance, while employing not more than a relatively small proportionof intermediate grain sizes, using a preponderant amount of magdensityfrom non-plastic material preponderantly magnesia, and a bondingsubstance, using nonplastic particles of relatively larger and smallergrain sizes, which consists in mixing larger nonplastic particlesretained on a 30 mesh per linear inch screen with smaller non-plasticparticles and a bonding substance, while employing not more than arelatively small proportion of intermediate grain sizes, using apreponderant .amount of magnesia in the mix, in molding the mix in moistcondition under pressure into a refractory shape, in drying therefractory shape and in sub--' jecti'ng the dried unburned refractoryshape to firing temperature in a furnace structure during use.

3. The method of making a refractory of high density from non-plasticmaterial preponderantly magnesia, and a bonding substance, usingnonplastic particles of relatively larger and smaller grain sizes, whichconsists in mixing larger nonplastic particles retained on a 20 mesh perlinear inch screen with smaller non-plastic particles and a bondingsubstance, while employing not more thana relatively small proportion ofintermediate grain sizes, using a preponderant amount of magnesia in themix, in molding the mix in moist condition under pressure into arefractory shape, in drying the refractory shape and in 'subjecting thedried unburned refractory shape to firing temperature in a furnacestructure during use.

4. The method of making a refractory of high density from non-plasticmaterial preponderantly magnesia, and a bonding substance, usingnonplastic particles of relatively larger and smaller grain sizes, whichconsists in mixing larger nonplastic particles retained on a 30 mesh perlinear inch screen with smaller non-plastic particles below 60 mesh perlinear inch and a bonding substance, while employing not more than arelatively small proportion of intermediate grain sizes, using apreponderant amount of magnesia in the mix, in molding the mix in moistcondition under pressure into a refractory shape, in drying therefractory shape and in subjecting the dried unburned refractory shapeto firing temperature in a furnace structure during use.

'5. The method of making a refractory of high density from non-plasticmaterial preponderantly magnesia, and a water soluble bond, usingnonplastic particles of relatively larger and smaller grain sizes, whichconsists in mixing larger nonplastic particles between 3 and 30 mesh perlinear inch in the proportion of to 65% with smaller non-plasticparticles below mesh per linear inch in the proportion of to 35%, andwith an appreciable amount but less than 5% of a water soluble bond,maintaining the mixture free from insoluble bond and incorporating apreponderant amount of magnesia in the mixture, in molding the mixturein moist condition under a pressure exceeding 1000 pounds persquareinch, in drying the mixture and in subjecting the dried unburnedmixture to firing temperature in a furnace structure during use.

6. The method of making a refractory of high density from non-plasticmaterial preponderantly magnesia, and a water soluble bond, usingnonplastic particles of relatively larger and smaller grain sizes, whichconsists in mixing larger nonplastic particles between 6 and 30 mesh perlinear inch in the proportion of 45 to 65% with smaller non-plasticparticles below 50 mesh per linear inch in the proportion of 55% to 35%,and with an appreciable amount but less than 3% of sodium silicate,incorporating a preponderant amount of magnesia in the mixture, inmolding the mixture in moist condition under a pressure exceeding 1000pounds per square inch, in drying the mixture and in subjecting thedried unburned mixture to firing temperature in a furnace structureduring use.

7. The method of making a refractory of high density from non-plasticmaterial preponderantly magnesia, and an organic bond, using non-plasticparticles of relatively larger and smaller grain sizes, which consistsin mixing larger non-plastic particles between 6 and 30 mesh per linearinch in the proportion of 45% to 65% with smaller non-plastic particlesbelow 50 mesh per linear inch in the proportion of 55% to 35%, and withan appreciable amount but less than 3% of an organic bond, incorporatinga preponderant amount of magnesia in the mixture, in molding the mixturein moist condition under a pressure exceeding 1000 pounds per squareinch, in drying the mixture and in subjecting the dried unburned mixtureto firing temperature in a furnace structure during use.

8. The method of making a refractory of high density from magnesia and abonding substance, using larger and smaller grain sizes, which consistsin mixing larger magnesia particles retained on a 30 mesh per linearinch screen with smaller magnesia particles and a bonding substance,while employing not more than a relatively small proportion ofintermediate grain sizes, in molding the mix in moist condition underpressure into a refractory shape, in drying the refractory shape and insubjecting the dried unburned refractory shape to firing temperature ina furnace structure during use.

9. The method of making a refractory of high density from magnesia and awater soluble bond, using relatively larger and smaller grain sizes,which consists in mixing larger magnesia particles between 3 and 30 meshper linear inch in the proportion of 45% to 65% with smaller magnesiaparticles below 50 mesh per linear inch in' the proportion of 55% to35%. and with an appreciable amount but less than 5% of a water solublebond, maintaining the mixture free from insoluble bond, in molding themixture in moist condition under a pressure exceeding 1000 pounds persquare inch, in drying the mixture and in subjecting the dried unfiredmixture to firing temperature in a furnace structure during use.

10. The method of making a refractory of high density from a mixture ofmagnesia and chrome containing more magnesia than chrome, and a bondingsubstance, using larger and smaller grain sizes, which consists inmixing together magnesia and chrome particles, with an excess ofmagnesia, using larger particles between 10 and 30 mesh per linear inchwith smaller particles below mesh per linear inch, in roughly equalproportions, and with a bonding substance, in molding the mixture inmoist condition under high pressure, in drying the brick thus formed andin placing the dry unburned brick in a furnace structure.

11. The method of making a refractory of high density from a mixture ofmagnesia and chrome containing more magnesia than chrome, and a watersoluble bond, using relatively larger and smaller grain sizes, whichconsists in mixing together magnesia and chrome particles with an excessof magnesia, using larger particles between 3 and 30 mesh per linearinch in the proportion of 45% to with smaller particles below 50 meshper linear inch in the proportion of 55% to 35%, and with an appreciableamount but less than 5% of water soluble bond, in molding the mixture inmoist condition under pressure exceeding 1000 pounds per square inch, indrying the mixture and in subjecting the dried unburned mixture tofiring temperature in a furnace structure during use.

12. A dry refractory body preponderantly containing magnesia, said bodyhaving low porosity, being in unfired condition and suitable for use inunfired condition, and comprising a bonding substance distributedthrough a densely compacted mixture of larger non-plastic particlescapable of being retained on a screen of 30 mesh per linear inch andsmaller non-plastic particles capable of passing through a screen of 60mesh per linear inch, in roughly equal proportions.

13. A dry refractory brick preponderantly containing magnesia, saidbrick having low porosity, being in unfired condition and suitable foruse in unfired condition, and comprising a densely compacted mixture ofabout equal proportions of larger non-plastic particles between 10 and30 mesh per linear inch and smaller non-plastic particles below 60 meshper linear inch and a water soluble bond.

14. A non-plastic refractory brick preponderantly containing magnesia,comprising about 55% of larger non-plastic particles between 10 and 30mesh per linear inch, about of smaller nonplastic particles below 60mesh per linear inch and a water soluble binder in dry form, the brickbeing of requisite cold strength for use in unfired condition.

15. A dry refractory brick preponderantly containing magnesia, saidbrick having low porosity, being in unfired condition and suitable foruse in unfired condition, comprising a densely compacted mixture ofbetween 45% and 65% of larger nonplastic particles between 3 and 30 meshper linear inch and between 55% and 35% of smaller nonplastic particlesbelow mesh per linear inch and an appreciable amount but less than 5% ofa water soluble bond in the mixture, and being free from insoluble bond.

16. A dry refractory brick preponderantly containing magnesia, saidbrick having low porosity, being in unfired condition and suitable foruse in unfired condition, comprising a densely compacted mixture ofbetween 45% and 65% of larger non-plastic particles between 3 and 30mesh per linear inch and between and 35% of smaller non-plasticparticles below 50 mesh per linear inch and an appreciable amount butless than 3% of sodium silicate in the mixture.

17. A dry refractory brick preponderantly containing magnesia, saidbrick having low porosity, being in unfired condition and suitable foruse in unfired condition, comprising a densely compacted mixture ofbetween 45% and of larger non-plastic particles between 3 and 30 meshper linear inch and between 55% and 35% of smaller non-plastic particlesbelow 50 mesh per linear inch and an appreciable amount but less than 3%of organic binder in the mixture.

18. A dry magnesia brick having low porosity, being in unfired conditionand suitable for use in unfired condition, comprising a denselycompacted mixture of between 45% and 65% of larger non-plastic particlesbetween 3 and 30 mesh per linear inch and between 55% and 35% of smallernon-plastic particles below 50 mesh per linear inch and an appreciableamount but less than 3% of water soluble bond in the mixture, and beingfree from insoluble bond.

19. A dry magnesia-chrome brick containing more magnesia than chrome,having low porosity, being in unfired condition and suitable for use inunfired condition, comprising a densely compacted mixture of between 45%and 65% of larger nonplastic particles between 3 and 30 mesh per linearinch and between 55% and 35% of smaller nonplastic particles below 50mesh per linear inch and an appreciable amount but less than 5% of watersoluble bond in the mixture.

RUSSELL P. HEUER.

